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21 May 1996 Practical and precise method for mask defect size measurement
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Abstract
An objective and practical method for accurate sizing of mask defects found with inspection tools is presented. Diameters of defects found on a KLA Instrument's 219e mask inspection tool were measured to an accuracy of 0.10 microns by using gray scale image information provided by the KLA machine. Final through-the-pellicle inspection may include defects which are smaller than specification. Precise and practical measurement of these defects is vital for objective disposition. Further, the ability to perform statistics on these measurements allows greater process improvement and inspection strategy tuning. Test defects were measured on a Verimask (a plate with programmed defects and 'standard' sizes for each defect, made by Dupont) and supplied as a calibration gauge for the measurement tool. Images of the defects were extracted from the video output of the KLA tool. A reference image was derived by averaging the light intensity in the region surrounding the defect. In cases where the surrounding area was non-uniform (edge defect), a separate reference image was extracted from the KLA tool. Then the area of the defect was measured by subtracting the reference image from the original and measuring the total difference in light energy in the region of the defect. This total light difference was scaled to the calibration measurements by using a quadratic least squares fit. Separate calibration curves are used for spots, holes, intrusions, and extensions, correcting for optical characteristics of the system and likely skews in the reference measurements.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Steve George and Peter Fiekowsky "Practical and precise method for mask defect size measurement", Proc. SPIE 2725, Metrology, Inspection, and Process Control for Microlithography X, (21 May 1996); https://doi.org/10.1117/12.240082
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